Variable wagtailPreviewPluginConst

Axe plugin registry for interaction between the page editor and the live preview. Compared to other aspects of Axe and other plugins,

• The parent frame only triggers execution of the plugin’s logic in the one frame.
• The preview frame only executes the plugin’s logic, it doesn’t go through its own frames. See https://github.com/dequelabs/axe-core/blob/master/doc/plugins.md.